The present invention relates to a method of controlling an image recorder of the type forming a toner image on a photoconductive element, or image carrier, transferring the toner image to a recording medium, and fixing the toner image on the medium. More particularly, the present invention is concerned with an image recorder control method capable of detecting a medium jammed a transport path and then slipped out of the path in the event of removal.
An electrophotographic copier, facsimile transceiver, laser beam printer or similar electrophotographic image recorder is extensively used today. A predominant type of electrophotographic copier, for example, has a transport path defined in a lower portion thereof and extending substantially horizontally to an image transfer station. A recording medium in the form of a paper sheet is driven along the transport path to contact the surface of a photoconductive element at the image transfer station, whereby a toner image is transferred from the photoconductive element to the sheet. The paper sheet carrying the toner image thereon is further transported to a fixing station.
On the other hand, there is an increasing demand for a miniature copier and, therefore, an implementation for promoting efficient use of the space available in a copier. In this sense, the transport path extending horizontally in a copier as stated above is not desirable. For this reason, an electrophotographic copier having a substantially vertically extending transport path has been recently developed. In this kind of copier, a developing unit, image transferring and paper separating unit and other process units are arranged along the vertical transport path. A paper sheet is transported along such a path to an image transfer station and caused into contact with the surface of a photoconductive element there. As a result, a toner image is transferred from the photoconductive element to the paper sheet. When the photoconductive element is implemented with a belt, for example, it is held in an inclined position to adjoin the vertical transport path while the image transferring and paper separating unit is located to face a part of the belt that faces the belt. A paper sheet transported along the vertical transport path to the image transferring and paper separating unit is caused into contact with the surface of the belt.
In an image recorder having a vertical transport path as described above, a paper sheet coming out of the image transferring and paper separating unit and carrying a toner image thereon is driven substantially vertically along the path toward a fixing unit. At this instant, since the toner image on the paper sheet has not been fixed yet, it is not allowable to nip the paper sheet by rollers or similar members at both sides thereof. Usually, therefore, only the back or non-imaged side of the paper sheet is held by rollers. When a paper sheet jams the transport path between the belt and the image transferring and paper separating unit, the unit is moved away from the belt to remove the paper sheet. So long as the paper sheet to be removed has a relatively large size, it will have been caught at the leading edge thereof by a register roller pair located at the inlet of the developing unit or caught at the trailing edge thereof by rollers of the fixing unit. Such a sheet, therefore, will remain on the transport path during and even at the end of the removing operation. However, when the size of the jamming sheet is relatively small, it is likely that neither the leading edge nor the trailing edge thereof has been retained by the register roller pair of the rollers of the fixing unit. Then, at the time when the image transferring and paper separating unit is moved away from the belt, the paper sheet is apt to drop along the surface of the belt and thereby slip out of the transport path. Should the image recorder be driven again with the dropped paper sheet being unnoticed by the operator, the sheet would cause a serious trouble to occur. Specifically, when the paper sheet drops into the cleaning unit or the developing unit, it causes a cleaning agent or a developer to overflow the associated unit. In such a case, the image recorder cannot be restored to normal unless the developer is replaced or all the parts and elements surrounding the belt are cleaned up. Moreover, the jamming paper sheet is apt to physically damage the belt. While a pawl or a blade made of resin is an anti-drop approach proposed in the past, it is not satisfactory when it comes to an image recorder which has to operate at high speed and be miniature.